Directional aerial system



Jan. 16, 1940- E. c. CORK ET AL 4 2,187,015

DIRECTIONAL AERIAL SYSTEM Filed June 18, 1938 4 Sheets-Sheet 1 .epwmoCECIL CORK AND /1 BY 05 PH mos PAWSEY ATTORNEY.

Jan. 16, 1940. g, am ET AL 2,187,015

, DIRECTIONAL AERIAL SYSTEM Filed June 18, 1938 4 Sheets-Sheet 2INVENTORS BY 05' PH L/JDE PAWSEY' A TTORNEY.

.Jan. 16, 1940. E. c. CORK ET AL DIRECTIONAL AERIAL SYSTEM Filed June18, 1938 4 Sheets-Sheet 3 I NV EN TO RS EDWARD CfC/L CORK/MID Jan. 16,1940.

E. c. CORK ET AL 2,187,015

DIRECTIONAL AERIAL SYSTEM Filed June 18, 1938 4 Sheets-Sheet 4 X Y B 3 2EL; X 1 1 INVENTORS ATTORNEY. V

Patented Jan. 16, 1940 PATENT OFFICE DIRECTIONAL AERIAL- SYSTEM EdwardCecil Cork, Ealing, London, and Joseph Lade P'awsey, Hillingdon,England, assignors to Electric & Musical Industries Limited, a

British company Application June 18, 1938, Serial No. 214,436 In GreatBritain June 26, 1937 3 Claims.

This; invention relates to directional transmittingor receiving aerial.systems, thedirectional propertiesbeing used in the case of transmittersto radiate signals in a predetermined direction and in the case ofreceivers, for the purpose of improving the signal to noise ratio; byincreasing the pick-up signalandlreducing the unwanted interference. "Inat'elevision receiving system for example, it may happen that intenseinterferencemay be set up'b'y apparatus suchas that employed fordiathermy purposes. Providing that the angle between the wanted andunwanted signals isgreater than afew degrees, it is. possible tosuppress the interference while retaining the wanted signal.

@In. such cases it is highly desirable. that it should be..-possible; toarrange that the region of minimum. pickup; in the directional diagramof an aerial array is insuch; a direction that there is a minimum. ofreceptiomand preferably a total suppressionyof the unwanted 'signaland amaximum of reception of the wantedsignal.

- One object"v of the present invention is to provide electrical meanswhich may be arranged so that. the region of minimum pick-up in thedirectional'diagram of a directional receiving-aerial system is directedto'thesource of interference. In another set of circumstances it may befound that-on the re-erection of an aerial array at another site, thesituation of the region of minimum pick-up in the directional diagramwhich has been found satisfactory under ideal conditions for thesuppression of interference is poor and displaced-due to the'presence oflocal objects causing a distortion of the field;

A further object of the invention, therefore, is to provide forselecting andimproving the minimumpick-up region by electrical means tocorrect for local irregularities. Itis a desirable feature that in:combination with means of observation such as for example, a televisionreceiver,' the adjustment of the minimum referred to should be capableof variation in proximity to the receiver, so the reduction ofinterference may be observed and the interference eliminated as itarises.

. Another object of the invention is to provide a directionaltransmitting system in which the region of maximum radiation in thedirectional diagram is in the direction in which it'is desired totransmit signals.

Accordingto the present invention a directional aerial system includes.two aerials the energy in which is passed through an amplitude control.arrangement to or from a common channel, phase adjustment being effectedin one of the aerial leads in order to control the phase of signalspassedto or from that aerial relatively to those passed to or from theother aerial to the common channel. The phase adjustment may, forexample, be effected by inserting selectedlengths of conductorin thelead from the aerial to the amplitude controlling arrangement associatedwith that aerial, and provision may be made for continuously effecting,fine adjustment of the phase displacement. Amplitude control may beeffected by means ofa variable resistance or by variable couplingtransformer arrangements connected between the two aerials'and thecommon I Figures-l and 2 are explanatory diagrams and t Figure 3 showsdiagrammatically one for'm of aerial system embodying the invention,

Figure 4 shows a modified arrangement of Figure 3. Figures 5, 6 and 9show further modifications of the present invention, while. Figure 7shows a type of goniometer which may .be used with the. presentinvention andv whichisparticularly adaptable to .ultra short waves, andFigure 8 shows the electrical equipment of the goniometer shown. inFigure '7. Y

Referring to Figure 1 of the drawings, two receiving aerials A1 and A2-are shown spaced apart at adistance d, and it is. assumed that asignalis arriving at an angle 0 tothe line between the aerials. There isaphase difference between the signals induced in the aerials due to the.path difference A1C equal to radians. If it is assumed that there is afurther phase difference due to the aerial feeders and the phaseadjusting arrangements at one or the other of the aerials, the phasedifference being indicated by (p and the amplitudes are adjusted toequality, it can be shown that the picked'up signal has an amplitude ofwhich has a maximum value at Hence A cos 6,,,-,,. cos 0 a It willtherefore be seen that if the spacing between the aerials is great (asmall) the angle between the maximum and minimum of a loop is small,which indicates a large number of narrow loops.

If, therefore, the interference and signal differ in angle by a smallamount, it is desirable to space the aerials apart by a considerabledistance. It is preferred to make use of a suitable condition such thatthe interference falls on a region of zero pick-up in the directionaldiagram of the aerial, while the signal falls within the adjacent regionof maximum pick-up.

For example, if the signal and interference differ in direction ofarrival of 10 degrees and the direction of the signal is perpendicularto the line of the aerials (i. e. cos emax o) then the spacing to givethis condition would be 10. Elly In order that the nature of the phaseand amplitude control arrangements may be more fully understood,reference will now be made to Figure 2 of the accompanying drawingswhich shows two aerials A1 and A2 and feeder lines I and 2 which areapproximately matched to the aerials. The dotted rectangles 3 and 4contain phase controlling and amplitude controlling arrangementsrespectively. The phase controlling network includes sections of feeder5 which may be selectively included in or disconnected from the line byplug-in contacts or by a switching device. The selection of the lengthsof feeder included enables phase adjustment to be effected in steps of60 between 0 and 360 and finer adjustment of phase difference betweenthe signals received may be effected by the provision of a tuned circuitincluding inductance 6 and capacity l, which introduces a variable phasedifference controllable by the condenser E of approximately plus orminus 45.

The amplitude control device consists of a resistance 8 connected atopposite ends to the aerials A1 and A2, and provided with a tapping 9connected to a receiver not shown in the drawings.

A practical form of directional aerial system is shown in Figure 3 whichincludes two aerials A1 and A2 and a dial switch Hi. which serves toconnect selected lengths of line H, l2 or l3 for coarse variation of thephase shift desired.

A parallel tuned circuit M is arranged at a point A a quarter of awavelength away from the point B at which the receiver is connected, thetuned circuit serving to effect fine adjustment of the degree of phaseshift. It is known that a parallel tuned circuit M connected as shown isequivalent to a series tuned circuit arranged at the point B and has theadvantage of allowing one side of the variable condenser forming part ofthe tuned circuit to be connected to earth.

A variable resistance I5 is connected at a point also a quarter of awavelength away from the point B for the purpose of controlling theamplitude of the signals fed from one of the aerials to the receiver. Inthis case also the parallel connected resistance is equivalent to aresistance connected in series at the point B, but again the parallelconnection enables one side of the resistance to be connected to earth.A changeover switch l6 enables the resistance IE to be transferred tothe aerial which has induced in it the greater undesired signal.

If it is more convenient the phase and amplitude control arrangementsmay be divided into sections on either side of the point B at which thereceiver is connected, but the arrangement illustrated in Figure 3 ofthe drawings possesses the merit that the relative phase and amplitudecontrols are independent.

In the modified form of Figure 3 shown in Figure 4 the tuned circuit llof Figure 3 has been replaced by two identical tuned circuits I1 and I8and a resistance l9 equal in magnitude to the characteristic impedanceof the feeder (Z0) has been added in series with the tuned circluit 18.The variable condensers of the tuned circuits IT and i8 are gangedtogether for simultaneous adjustment.

In a similar manner the resistance l5 of Figure 3 has been replaced inFigure 4 by two equal variable resistances 20 and 21 connected to pointsin the feeder a quarter of a wavelength apart. The resistances 20 and 2|are also ganged for simultaneous adjustment. A resistance 22 isconnected in series with the variable resistance 2| and has a valueequal to the characteristic impedance of the feeder (Z0).

It is a property of the network including the resistances 20, 2! and 22that when matched at the aerial end, the input impedance at the point ofconnection of the resistance 22 to the feeder, is equal to the value ofthe characteristic impedance of the feeder independently of the value ofthe resistances 20 and 2!.

Variation of the resistances 20 and 2| serves to vary the attenuation ofthe signals from the aerial to which they are connected without changeof phase. tuned circuits l1 and I8 and the resistance I 9 has a constantinput impedance at the point at which the resistance [9 is connected tothe feeder and variation of the ganged condensers of the tuned circuitsfrom the tuned position varies the phase of the signals received fromthe aerial to which they are connected substantially withoutattenuation. Coarse phase adjustment is provided by a rotary switch 23which serves to select tapping points along a conductor 24 which is onehalf a, wavelength long.

Referring, now, to Figure 5 of the accompanying drawings, a modificationis shown in which coarse phase adjustment is effected by connectingaerial A1 through a switch 25 to a variable tapping point in a length offeeder 26 which may be about one wavelength long. Fine phase adjustmentis effected by the tuned circuit 21, amplitude control being effected bythe variable resistance 28. The lead 29 is connected to a receiver as inthe preceding arrangements. The length of feeder 26 is terminated by aresistance 30 approximately equal in value to the character isticimpedance of the length of feeder 26. The resistance 3|! allows a verysimple tapping switch Similarly, the network including the l 25 tobeused without variations dueto the varying length of the dead end of thelengthof mitting' aerials, In both the cases-of transmitting andreceiving systems, it is of coursedesirable to avoid waste of power asmuch as possible, and as the amplitude control by means of variableresistance does involve waste of power, the following methods ofefiectingamplitude control ofiers alternatives which may be adopted andare of particular advantagein the case of transmitting systems.

Thus referring toFigure 6 of the drawings an is varied by switching inmore or less turns of the coil L3 the relative amplitudes in the aerialsis affected. It is desirable that L1 and L2 should not have directcoupling with each other and that as the coupling M1 and M2 varies, theload on the transmitter should remain constant.

This latter condition requires for similar aerials that Both of theseconditions are satisfied if the m M =a constant.

coils L1 and L2 are arranged at right angles to each other and the coilL3 is angularly disposed with respect to them in a manner of a radiogoniometer. p 1

The coils L1, L2 and L3 may take the form shown in Figure 7, theelectrically equivalent arrange ment being shown in Figure 8. The coilsL1 and L2 are made from a piece of copper sheet, cruciform in shape, thelimbs of the cross being bent up to form a box like structure as shown.The

coil L3 is formed of strip coppernarrower than the strips forming thecoils L1 and L2 and is mounted on a hollow shaft 32 so as to be r0.-tatable within the box formed by the strip coils L1 and L2. The leads 33to the coil L3 pass through the hollowshaft 32. The relation between thephysical form of the coils and the e1ectrical circuit as shown in Figure8 the points X--X1 and YY1 having corresponding positions in the twofigures.

The values of L1, L2, M1, M2 may be selected to give a unitytransformation ratio so that the same feeder may be used throughout andthe feeder to the transmitter or receiver remaining matched for anysetting of the coil L3. Alternatively other transformation ratios may beobtained by adjustment of the coil dimensions. Each coil is individuallytuned and the appropriate feeder connected in parallel across the tunedcircuit formed.

The arrangement described with reference to Figures 7 and 8 is adaptedto use balanced feeders but it is probable that in view of the very lowimpedance circuits obtained with this construcimpairing theeffectiveness of the device:

An alternative method of effecting amplitude control is shown in Figure9, in which the coupling arrangement shown in Figures 7- and 8 isreplaced by a tapped half wavelength line. The aerials A1 and A2 areconnected 'to points. on. a half wavelength line 33. short circuited ateach end and connected at its center to a transmitter .or receiver byalead 34. The tapping points and 35 are maintained. at one quarter of awave:- lcngth. apart and the variation of amplitude: is obtained bymoving the tapping points simultaneously along the line The inputimpedance at the mid point P of the line is where R is the resistance'ofeach aerial assumed to be equal and Z0 the characteristic impedance ofthe half wavelength line.

If the reactance is tuned out as indicated by the condenser 31 thedevice forms a unity ratio transformer. The relative amplitudes in theaerials A1 and A2 is given by tan 6. For a small range of amplitudecontrol the reactance will not materially change assuming Z0 to besuitably selected so that the system remains substantially tuned. 1

The invention may be applied not only to dipoles and similar aerials,but generally to directional systems. It could, for example, be used ina system combining different types of aerials to produce severalcontrollable regions of minimum pick-up or radiation in a directionaldiagram. In the case of reception, it will be seen that the arrangementdescribed enables the direction of reception of the array to be changedbyvelec'trical means, and complete suppression of any given fixed sourceof interference may be effected even in the presence of distortion ofthe field caused by neighboring objects. It will be seen also that theinterference suppressing arrangements are located at the receiver sothat interference from a given source may be suppressed when it arises.

Having now particularly described and ascertained the nature of our saidinvention and in what manner the same is to be performed, we declarethat what we claim is:

1. A directional aerial system including two aerials, an aerial leadconnected to each aerial,

a common channel coupling said leads to a transducer, means connected toone of said leads for varying the phase of signals therein with respectto signals in the other lead and means in the other of said leads forvarying the amplitude of signals therein with respect to the signalsinsaid first lead, said first means comprising an inductance and acapacity connected in parallel and connected to a point in said aeriallead one quarter of a wavelength from'the point of connection of saidleads to said common channel and said second means comprising a variableresistance connected at a point one quarter of a wavelength from saidpoint of connection of said lead to said common channel.

2. A directional aerial system including two aerials, an aerial leadconnected to each aerial,

a common channel coupling said leads to a transducer, means connected toone of said leads for varying the phase of signals therein with respectto signals in the other lead and means in the other of said leads forvarying the amplitude of signals therein with respect to the signals insaid first lead, said first means comprising an tion, concentric feedersmay be used without inductance and a capacity connected in parallel andconnected between a point in said first aerial lead one quarter of thewavelength from the point of connection from said leads to a commonchannel and ground, said second means comprising a variable resistanceconnected between a point one quarter of a wavelength from said point ofconnection in said other aerial lead and ground.

3. A directional aerial system including two aerial leads connected toeach aerial, a common channel coupling said leads to a transducer, meansconnected to one of said leads for varying the phase of signals thereinwith respect to signals in the other lead, and means in the other ofsaid leads for varying the amplitude of signals therein with respect tosignals in said first lead, said first mentioned means comprising a pairof identical parallel tuned circuits spaced apart by one quarter of thelength of the operating wave and connected between ground and said firstaerial lead, a resistance equal in magnitude to the characteristicimpedance of said lead being connected in series with one of saidparallel tuned circuits, said second means comprising a pair of equalresistances spaced apart by one quarter of the length of the operatingwave and connected between ground and said other aerial lead, aresistance equal in magnitude to the characteristic impedance of thatlead being connected in series with one of said resistances whereby thephase of the signals in one of said leads may be varied withoutvariation of the attenuation, and the attenuation of the signals in theother of said leads may be varied without change of phase in the signalsin that lead.

EDWARD CECIL CORK.

JOSEPH LADE PAWSEY.

